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Tan Y.,Tongji University | Wang D.,Shanghai Geotechnical Investigations and Design Institute Co.
Journal of Performance of Constructed Facilities | Year: 2015

Via analyzing the field instrumentation data, this study examines the structural behaviors of the multipropped diaphragm wall for excavation of the outer rectangular pit. The circumferential stresses in waler beams as well as boundary beams were closely related to the corresponding wall deflections. Braced struts might lead to stress-concentration in the retaining structures. Because of the uneven vertical movements of floor slabs, boundary beams suffered bending stresses. The stresses in interior columns were governed by the weights of cast floor slabs and rebounds of basal soils. The significant upward movements of interior columns and heavy floor slabs indicate that the released stresses due to soil removal outweighed the heavy weights of the retaining structures. The excavation-induced lateral loads against the retaining wall were mainly carried by the rigid floor slabs and concrete beams, which were up to 10 times or more those carried by the temporary propped struts. The comparison between the field data and the design analysis results shows that the theoretical beam-on-elastic-foundation design models can make a relative reasonable estimation on the wall deflections for the unpropped circular diaphragm wall, but highly underestimated the wall deflections of the multipropped rectangular diaphragm wall. The potential adverse effects resulting from structural deficiencies (e.g., openings on floor slabs for soil discharge) and pit-size effects on weakening the capabilities of cast floor slabs or braced struts to constrain wall deflection should be taken into account in design analysis of top-down excavations. © 2014 American Society of Civil Engineers. Source


Yu D.-H.,Tongji University | Yin J.,Shanghai Geotechnical Investigations and Design Institute Co.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2010

The composite soil nailing wall is a kind of support for foundation pits. This method has been widely used in the project practice in recent years because of its excellent behaviors and low cost. The deformation and failure mechanism of composite soil nailing wall and the method to calculate its overall stability of foundation pits in Shanghai soft clay are discussed. The FEM is introduced to analyze the displacement and overall safety of the composite soil nailing wall. A case of composite soil nailing wall is employed to validate the proposed FEM. It is suggested that the displacement and overall safety factor should be considered together. Source


Tan Y.,Tongji University | Lan H.,Shanghai Geotechnical Investigations and Design Institute Co.
Journal of Performance of Constructed Facilities | Year: 2012

To ensure the safety of adjacent 16.7-m-high concrete frame structures (cooling towers) and buried pipelines in service during installation of 83 prestressed high-strength concrete (PHC) pipe piles, the behavior of the ground, the buried pipelines, and cooling towers was monitored by a comprehensive instrumentation program. The field measurements included the following: (1) time histories of the particle velocities and corresponding Fourier spectra in three mutually perpendicular directions at various pile penetration depths and (2) vertical and horizontal movements of the buried pipelines caused by pile installation. Based on the analysis of the field data, the following major findings were obtained: (1) unlike the driving of prestressed concrete piles or cast in situ piles, the vibration velocity in the vertical direction was not greater than that in the plane during PHC pipe pile driving; (2) the amplitudes of the peak particle velocities were relatively independent of the pile penetration depths because of the complex soil conditions; (3) both the ground and the concrete structure experienced primarily high-frequency vibrations, which attenuated rapidly over time; (4) during the pile driving, only slight vibration amplification was observed at the upper levels of the existing concrete frame structure as a result of the soil-structure interaction - the concrete structure had a much wider frequency band (around 0-300 Hz) than the ground (around 0-100 Hz); and (5) the method of installing the piles close to the existing facilities before installing those a distance away effectively mitigated the potential adverse effects on the buried pipelines. © 2012 American Society of Civil Engineers. Source


Tan Y.,Tongji University | Wang D.,Shanghai Geotechnical Investigations and Design Institute Co.
Journal of Performance of Constructed Facilities | Year: 2015

The excavation of a large-sized foundation pit for one skyscraper in Shanghai required installation of a 100-m diameter unpropped circular diaphragm wall at the pit center first, followed by installation of a multipropped rectangular diaphragm wall at the periphery. Due to the limited paper length, this study just focuses on the structural behaviors of the inner circular wall and those of the outer rectangular wall will be presented in a companion paper. The circular diaphragm wall exhibited apparent spatial arching effects during excavation and only slight differences were observed in its maximum lateral movements along the circumference. Like braced struts, waler beams mainly carried the load due to soil removal in the proximity. In contrast, the circular diaphragm wall carried the hoop stresses due to soil removal throughout the excavation. The vertical bending stresses in diaphragm wall panels were symmetric about their neutral axes. Although the adopted remedial measure effectively mitigated their potential adverse effects on wall deformations, structural deficiencies (e.g., diaphragm wall panels encountered the existing long driven piles at several locations) resulted in some detrimental effects (e.g., tension stress development in concrete and uneven stress distributions in retaining structures). Throughout the construction, the stress development patterns in concrete corresponded well with those in reinforcing rebars, which indicated that the retaining structures were not overstressed. The comparisons between the design analysis results and the field measurements show that the adopted beam-on-elastic-foundation method can make relatively reasonable estimation on excavation-induced deflections of the unpropped circular retaining wall. © 2014 American Society of Civil Engineers. Source


Yin J.,Shanghai Geotechnical Investigations and Design Institute Co.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2010

The theoretical foundation of the hardening soil model (HSS model) with small strain stiffness is introduced. The method to determine the parameters of the HSS model is proposed. The experimental parameters of the HSS model of Shanghai soft clay are given. Two projects of deep foundation excavation in Shanghai are analyzed by use of the fluid-solid FEM. The results of numerical analysis agree with the measured data. The feasibility of the HSS model and the accuracy of the recommended parameters are validated. Source

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